This disclosure relates to generating electromagnetic forces through an electromagnetic actuator and, more particularly, to generating electromagnetic forces through an electromagnetic actuator with flux feedback control.
In certain electromagnetic actuators, such as, for example, electromagnetic actuators used in active magnetic bearings, an electromagnetic force may be assumed to be a known function of a control current. It may be desirable for this function to be a linear function in order, for instance, to simplify an algorithm for controlling the electromagnetic force. This linear function may be achieved by introducing a bias flux. The assumption that the electromagnetic force may be a known function of the control current may not, however, be entirely accurate. For example, the electromagnetic force may also depend on a rotor position due to the negative stiffness directly associated with the presence of the bias flux. Further, the electromagnetic force may depend on a magneto-motive force (MMF) drop in one or more soft-magnetic parts of a magnetic circuit of the electromagnetic actuator, which may increase as the soft-magnetic part materials are brought closer to saturation. This may make the electromagnetic force a non-linear function of the current even if the bias flux is used. Also, the force may further depend on a frequency, especially when the soft-magnetic parts of the magnetic circuit are not laminated as in the case of, for example, an axial actuator.